Radiative heat transfer in processing of glass-forming melts

The paper summarizes the findings of a study on mathematical modeling of heat transfer in glass melts using the commonly employed diffusion or Rosseland approximation (R) for optically thick media and the more general, spectral discrete ordinates (DO) approach. The systems considered were the melting of an ultra-clear glass in a furnace (optical thickness 10) and heat transfer in 2 glass melts with different levels of iron oxide flowing through a delivery channel (optical thicknesses of 17 and 80). The results showed that the use of the R approach for modeling heat transfer in the ultra-clear glass will lead to serious errors in the prediction of important practical parameters such as the refractory temperature, energy efficiency, and the quality of glass melt. The results for the channels showed that differences between the 2 thermal radiation models began to narrow as the optical thickness value approached 17. The paper also presents brief reviews of high-temperature absorption spectra of commercial glass melts and the theoretical background on thermal radiation in participating media. In addition, a relatively simple system involving 1-dimensional radiation heat transfer in a participating medium is used to illustrate the implications of using the diffusion approximation.